Multi-objective Optimization Of Aerodynamic Characteristics Of Auto Body Based On CFD

Body aerodynamic performance is an important performance of the car,which directly affects the fuel economy,operational stability,comfort and power of the car.At present,in the automotive body design and development process,the requirements for modeling,simulation and optimization of its aerodynamic characteristics are increasing.In this work,combined with parametric modeling,computational fluid dynamics(CFD)simulation,experimental design,response surface model and intelligent optimization algorithm,an automatic design flow for multi-objective optimization of aerodynamic characteristics in the body design stage is established and applied to MIRA fastback model body.The results show that the automatic optimization process established in this paper can achieve multi-objective optimization of aerodynamic drag and crosswind stability.At the same time,labor cost and computing resource can be saved and the design cycle can be shortened.Firstly,the MIRA fastback parametric model is established based on Pro/E,and the model is driven by the size parameter.To automate the entire process,it is important to ensure that the design variables are continuously variable within the design domain.Secondly,the aerodynamic simulation of MIRA fastback front windward condition and condition with yaw angle 15° is carried out,and the simulation results are verified by benchmarking.The aerodynamic drag coefficient of the frontal windward condition and lateral force coefficient of condition with yaw angle of 15° are selected as the optimization targets.By analyzing the flow field outside the body such as streamline,the turbulent kinetic energy,and the pressure distribution characteristics of the vehicle body surface,it is determined that the hood angle,the front windshield angle,the rear wind window inclination angle and the trunk upturn angle are taken as the design variables.Thirdly,the sample point(DOE point)is generated by design of experiment;the CAD model corresponding to the DOE point is generated in batches based on the Pro/E parametric modeling software;the ICEM and Fluent are called in the DOS environment to face all the DOE points.The aerodynamic simulation of working condition and yaw angle 15° condition is carried out,and the aerodynamic drag coefficient and lateral force coefficient are extracted respectively.The DOE matrix is established,and the DOE matrix is taken as the initial population to establish the response surface model.Finally,based on the response surface model,the influence trend and influence sensitivity of the design variables on the optimization targets are analyzed.Combined with the genetic optimization algorithm,the Pareto frontier curve of the multi-objective optimization problem of the aerodynamic characteristics of the vehicle body is obtained,which provides a reference for the aerodynamic optimization design of the vehicle body.